[blasdel]

IE9 could always install it as a DirectShow filter on Vista like the Media Center stuff does. Google Chrome loosely bundles ffmpeg, which you can just swap out with one that isn't denuded. I don't think you can install Safari on Windows without Quicktime.

You'd ideally support every codec under the sun by falling back to the platform's API. That "choice" would probably lead to people being forced to support one particular codec (h.264 for now), but it means that they don't have to pay for it. It also takes it out of the total control of the browser vendors — so it provides a path for Dirac/etc. to take off in the future.

There's also the ability for minority codecs to persist without gross transcoding (you can always fall back to a download link + VLC, which is what you had before). One of the worst things about the Theora debacle is that nearly all of the video out there is extra-lossily transcoded from more efficient files.